Method and system for structured programmed input/output transactions

ABSTRACT

Disclosed is a structured model for developing PIO code and for performing PIO transactions. This model of structured PIO transactions provides a framework with default behaviors. Developers need only provide a minimal amount of configuration information and can then characterize subsequent PIO transactions in terms of a profile, thus reducing the amount of detailed and often redundant information that developers need to provide for each PIO transaction. In some embodiments, the PIO transaction model is expressed in terms of object-oriented programming constructs. In one example, a PIO enabler object captures general PIO operational parameters and manages underlying operating system objects and behavior. When device manager software receives an input/output request that involves a PIO data transfer, the device manager constructs a PIO transaction object that represents the PIO work request. During the processing of the PIO transaction, the PIO transaction object maintains state and status information.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is related to another U.S. Patent Application, “Method and System for Structured DMA Transactions”, filed on Nov. 10, 2004.

TECHNICAL FIELD

The present invention is related generally to programmed input/output (PIO) transactions in computing systems, and, more particularly, to structured PIO transactions.

BACKGROUND OF THE INVENTION

PIO is a set of techniques for moving data from one area of memory in a computing device to another area (usually on a different piece of hardware). The central processing unit (CPU) of the computing device is used throughout a PIO operation because the transferred data all pass through the CPU. Because of this intensive CPU use, and because of the overhead necessary to program the CPU before the transfer, PIO has in many scenarios been replaced by the more efficient (because less CPU-intensive) techniques of DMA (direct memory access). PIO, based on simpler digital logic, still has its place, however, where lower memory transfer rates are acceptable.

Programming PIO transactions is complicated and often confusing. Some confusion arises because different operating systems impose different requirements on software developers who write code for PIO transactions. These developers may have only incomplete knowledge of the PIO requirements and capabilities of a device. Also, the developers may have neither the time nor the inclination to master all of the details of a given device's PIO transactions. In consequence, each developer tries to use only as much of a device's PIO capabilities as is strictly necessary for his tasks. Code supporting PIO transactions is thus implemented in an ad hoc fashion which invites errors and inefficiencies and which does not provide a stable basis for future development.

The resulting situation is that PIO transactions often run at a level of efficiency lower than would otherwise be possible, and ill formed PIO transactions can slow down or even jeopardize the stability of computing systems.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention provides a structured model for developing PIO code and for performing PIO transactions. This model of structured PIO transactions lessens the burdens on PIO software developers by providing a framework with default behaviors. Developers need only provide a minimal amount of configuration information and can then characterize subsequent PIO transactions in terms of a profile, thus reducing the amount of detailed and often redundant information that developers need to provide for each PIO transaction. If necessary, the developer can choose to override the profile for a specific PIO transaction.

In some embodiments, the PIO transaction model is expressed in terms of object-oriented programming constructs. In one example, the PIO transaction model is based on a PIO enabler object and on a PIO transaction object.

The PIO enabler object captures general PIO operational parameters and manages underlying operating system objects and behavior. The PIO enabler object hides details of these operating system objects from the developer; the operating system's specific needs are addressed through methods of the PIO enabler object. The PIO enabler object also holds default values for subsequent PIO transaction objects created to conduct PIO transactions.;

When device manager software (e.g., a device driver) receives an input/output request that involves a PIO data transfer, the device manager constructs a PIO transaction object that represents the PIO work request. The PIO transaction object references the PIO enabler object for default information. During the processing of the PIO transaction, the PIO transaction object maintains state and status information.

BRIEF DESCRIPTION OF THE DRAWINGS

While the appended claims set forth the features of the, present invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which:

FIG. 1 is a state-transition diagram for an exemplary DMA transaction model;

FIG. 2 is a schematic diagram generally illustrating an exemplary computing device that supports the present invention;

FIG. 3 is an execution workflow diagram for a DMA transaction;

FIG. 4 is an execution workflow diagram for initiating a DMA transaction;

FIG. 5 is a variation on FIG. 4 that specifies a non-standard maximum length for the DMA transaction;

FIG. 6 is an execution workflow diagram for a device manager-initiated DMA transaction;

FIG. 7 is an execution workflow diagram for the completion of a DMA transaction;

FIG. 8 is a variation on FIG. 7 that specifies the number of bytes actually transferred in the DMA transaction;

FIG. 9 is a variation on FIG. 8 with a DMA under-fill condition; and

FIG. 10 is an execution workflow diagram for a DMA transaction when resources (e.g., memory) are low.

DETAILED DESCRIPTION OF THE INVENTION

Turning to the drawings, wherein like reference numerals refer to like elements, the present invention is illustrated as being implemented in a suitable computing environment. The following description is based on embodiments of the invention and should not be taken as limiting the invention with regard to alternative embodiments that are not explicitly described herein.

In the description that follows, the environment surrounding the present invention is described with reference to acts and symbolic representations of operations that are performed by one or more computing devices, unless indicated otherwise. As such, it will be understood that such acts and operations, which are at times referred to as being computer-executed, include the manipulation by the processing unit of the computing device of electrical signals representing data in a structured form. This manipulation transforms the data or maintains them at locations in the memory system of the computing device, which reconfigures or otherwise alters the operation of the device in a manner well understood by those skilled in the art. The data structures where data are maintained are physical locations of the memory that have particular properties defined by the format of the data. However, while the invention is being described in the foregoing context, it is not meant to be limiting as those of skill in the art will appreciate that various of the acts and operations described hereinafter may also be implemented in hardware.

By applying a structure to memory transfer transactions, the present invention eases the software developer's task of setting up and coordinating those transactions. The imposed structure applies, mutatis mutandis, both to PIO transactions and to DMA transactions. Therefore, the following examples, drawn mostly from DMA implementations, serve as well to illustrate the concepts of PIO embodiments of the present invention. As PIO transactions are well known in the art, programmers of ordinary skill can easily modify these DMA examples to suit PIO transactions.

The exemplary embodiments of the present invention portrayed in the accompanying Figures model the structure of memory transfer transactions using an enabler object and a transaction object. The enabler object captures operational parameters specific to the type of memory transfer operation (e.g., PIO or DMA) to be performed and manages any underlying operating system objects. These operating system objects are hidden from software developers and are manipulated only through the methods of the enabler object. By so doing, the enabler object provides a consistent set of interfaces to different types of memory transfer transactions. Developers of device manager software simply declare the intended form of memory transfer operations used within their device managers and then initiate efficient memory transfers in a structured, transaction-oriented way. Various embodiments of the enabler object support some or all of the following features:

-   -   a transaction-based program model for memory transfer         transactions;     -   extension of input/output request processing into the DMA         domain;     -   management of mixed-mode DMA addressing (e.g., a 32-bit DMA         engine on a 64-bit platform);     -   management of scatter/gather lists;     -   full-duplex DMA operations: to-device DMA transfers operate         independently of from-device DMA transfers;     -   management of map registers; and     -   MDL (NDIS_BUFFER) chains such as NDIS (Network Driver Interface         Specification) drivers might expect.

A PIO or DMA developer chooses which enabler “profile” to use. For example, one DMA embodiment enumerates a set of supported profiles correlated to most PCI devices supporting DMA operations. A possible enumeration of profiles is as follows:

typedef enum_DMA_PROFILE { DmaProfilePacket32 = 0, DmaProfileScatterGather32, DmaProfilePacket64, DmaProfileScatterGather64, DmaProfileScatterGather32Duplex, DmaProfileScatterGather64Duplex, } DMA_PROFILE; For example, if a device supports scatter/gather DMA operations and has separate to-device and from-device DMA engines (e.g., it supports duplex operations) but only supports 32-bit addressing, then the developer could choose the profile DmaProfileScatterGather32Duplex when creating a new DMA enabler object.

The DMA enabler object is the container for a system's DMA adapter object. In general, any facilities which are supported by the DMA adapter are also supported by the DMA enabler. These facilities often include support for DMA operations (building scatter/gather or packet descriptors and mapping register allocation) and allocation of the Common Buffer.

The DMA enabler object is normally created during the StartDevice sequence. The developer may wish to consider the following factors during creation:

(a) The DeviceObject's Alignment Requirements value should reflect the alignment requirements of the device manager. This value is set in the DeviceObject prior to creating the DMA enabler object. Changes to the DeviceObject's Alignment Requirement value after creating the DMA enabler object have no effect on the new DMA enabler.

(b) The MaximumLength parameter of the DmaEnablerCreate function (used to create the DMA enabler object) usually represents the maximum transfer length allowable by a device manager. (An exception is for device managers that participate in NDIS driver configuration. See below.) This is the length of DMA transfers that are staged to the hardware. If a transfer is greater than MaximumLength, then the transfer is processed in multiple DMA transfers where each transfer is of MaximumLength or less.

(c) The device which the device manager controls may have additional hardware limitations as to the maximum number of scatter/gather elements it can handle in a single DMA transfer. If necessary, the DmaEnablerSetMaximumScatterGatherElements function is called to set the MaximumScatterGatherElements value. If used, this function should be called after the call to DmaEnablerCreate and before StartDevice finishes. If this value is not specified, then a default value is used which effectively disables any DMA enabler-based detection of a too fragmented data transfer.

Drivers that interface to NDIS's lower edge need to define their MaximumLength to accommodate the larger number of small MDLs which are usually passed down by NDIS. The typical NDIS_PACKET has five or six MDLs where each MDL contains a few tens of bytes of data. As an example, assume that a driver has a MaximumScatterGatherElements limit of 8 (HARDWARE_MAX_FRAG_COUNT). Then the formula for calculating the MaximumLength parameter for DmaEnablerCreate is: MaximumLength=PAGE_SIZE*HARDWARE_MAX_FRAG_COUNT

In a typical embodiment, only one DMA enabler object is created per device. However, a new DMA transaction object is created whenever a device manager receives an input/output request which involves a data transfer via DMA. The DMA transaction object references the DMA enabler object as part of its construction (so the DMA enabler object should be created first), and the DMA transaction object uses as defaults the value in the DMA enabler. During processing, the DMA transaction object represents the DMA transfer request, maintaining full state information.

For an exemplary DMA transaction object, FIG. 1 presents a state diagram and the application program interfaces (APIs) used to induce state transitions. In this example, there are two life cycle possibilities for the DMA transaction object. In the first possibility, the DMA transaction is deleted (100) when the DMA transfer is completed. In the second possibility, the DMA transaction object is pre-allocated once and then reused (102) for multiple DMA transfers.

The remainder of this specification provides details of embodiments of the DMA transaction object portrayed in FIG. 1.

Although many of the examples given in this specification are derived from implementations on Microsoft “WINDOWS” operating systems, the present invention may in fact be implemented on computing systems of any architecture. FIG. 2 is a block diagram generally illustrating an exemplary computer system that supports the present invention. The computer system of FIG. 2 is only one example of a suitable environment and is not intended to suggest any limitation as to the scope of use or functionality of the invention. The invention is operational with numerous other general-purpose or special-purpose computing environments or configurations. Examples of well known computing systems, environments, and configurations suitable for use with the invention include, but are not limited to, personal computers, servers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, and distributed computing environments that include any of the above systems or devices. In their most basic configurations, the computing system typically includes at least one processing unit 200 and memory 202. The memory 202 may be volatile (such as RAM), non-volatile (such as ROM or flash memory), or some combination of the two. This most basic configuration is illustrated in FIG. 2 by the dashed line 204. The computing system may have additional features and functionality. For example, it may include additional storage (removable and non-removable) including, but not limited to, magnetic and optical disks and tape. Such additional storage is illustrated in FIG. 2 by removable storage 206 and by non-removable storage 208. Computer-storage media include volatile and non-volatile, removable and non-removable, media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. Memory 202, removable storage 206, and non-removable storage 208 are all examples of computer-storage media. Computer-storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory, other memory technology, CD-ROM, digital versatile disks, other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage, other magnetic storage devices, and any other media that can be used to store the desired information and that can be accessed by the computing system. Any such computer-storage media may be part of the computing system. The computing system may also contain communications channels 210 that allow it to communicate with other devices, including devices on a network 212. Communications channels 210 are examples of communications media. Communications media typically embody computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism and include any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communications media include optical media, wired media, such as wired networks and direct-wired connections, and wireless media such as acoustic, RF, infrared, and other wireless media. The term “computer-readable media” as used herein includes both storage media and communications media. The computing system may also have input devices 214 such as a touch-sensitive display screen, a hardware keyboard, a mouse, a voice-input device, etc. Output devices 216 include the devices themselves, such as the touch-sensitive display screen, speakers, and a printer, and rendering modules (often called “adapters”) for driving these devices. All these devices are well know in the art and need not be discussed at length here. The computing system has a power supply 218.

FIG. 3 presents details of how an exemplary DMA transaction object progresses through the state machine of FIG. 1 during the processing of a DMA work request.

Step 300: In response to receiving a new Write Request on its input/output queue, the Write Dispatch routine calls DmaTransactionCreate to instantiate a new DMA transaction object. A handle to the new object is returned.

Step 302: The Write Dispatch routine calls DmaTransactionInitialize to set the initial parameters of the DMA transaction object. Note that other methods may be derived from DmaTransactionInitialize to initialize a DMA transaction object from special environments or from other non-DMA transaction objects.

Step 304: DmaTransactionExecute begins the initial DMA transfer. For example, when operating in scatter/gather DMA mode (as in the remainder of the example of FIG. 3), the kernel service BuildScatterGatherList is called with a DMA transaction-private function given as the “Execute Function” callback parameter. Note that DmaTransactionExecute is only used to begin the first DMA transfer. Subsequent DMA transfers are driven from DmaTransactionDmaCompleted as described below (step 318).

Step 306: The DMA transaction-private function (Execute) stages the callback into the device manager's PFN_PROGRAM_DMA function, ProgramDmaFunction.

The PFN_PROGRAM_DMA callback function programs a DMA transfer. This callback should be as focused as possible on programming the device to effect the DMA transfer, without mixing in other device manager operations unless absolutely necessary. The parameters passed to this callback are, respectively, a context, whether the DMA transfer is to or from the device, and a pointer to a scatter/gather list. If the DMA enabler object was created with a profile supporting scatter/gather operations, then the scatter/gather list may contain one or more SCATTER_GATHER_ELEMENTS. Otherwise, the scatter/gather list contains a single element.

Typedef BOOLEAN (*PFN_PROGRAM_DMA) ( IN DEVICE Device, IN PVOID Context, IN DMA_DIRECTION Direction, IN PSCATTER_GATHER_LIST SgList ); The PFN_PROGRAM_DMA callback is called at IRQL level DISPATCH.

If for some reason, the PFN_PROGRAM_DMA callback cannot initiate the DMA transfer, then the DMA transaction should be aborted. When necessary, this should be done as soon as possible, to allow the scare resources consumed by the DMA transaction (map registers in particular) to be made available to others.

Step 308: ProgramDmaFunction's input is a kernel-provided scatter/gather list. This method translates this list into a device-dependent scatter/gather list and programs the device registers to start the DMA transfer.

Step 310: When the device completes the DMA transfer operation, it sets its Command/Status Register (CSR) and generates an interrupt.

Step 312: The device manager's ISR (Interrupt Service Routine), IsrFunction, detects that the interrupt is signaling the completion of a DMA transfer operation and schedules the device manager's DPC (Deferred Procedure Call) routine.

Step 314: The device manager's DPC routine, DpcFunction, determines which DMA transaction is indicated by the interrupt (there could be several concurrent DMA operations) and retrieves the associated DMA transaction object handle.

Step 316: With the DMA transaction object handle, DmaTransactionDmaCompleted is called to indicate to the DMA transaction object that this DMA transfer has completed. This method call allows the DMA transaction object to continue processing the DMA transaction.

Step 318: If DmaTransactionDmaCompleted determines that more DMA transfers should be staged, then it calls a DMA transaction-private function, StageDmaTransfer, to begin the next DMA operation. StageDmaTransfer calls the kernel-service BuildScatterGatherList again but with parameters set to transfer the next section of data.

Step 320: The Execute function, common to step 306, forms the top of the DMA transfer loop (steps 306 through 320) which continues until all of the data identified in the DMA transaction have been transferred.

Step 322: The DmaTransactionDmaCompleted method returns an indication as to whether all of the DMA transfers have been completed. When more DMA transfer operations are needed, then a TRUE value is returned, and status is set to MORE_PROCESSING_REQUIRED. When a FALSE value is returned (and a non-MORE_PROCESSING_REQUIRED status is set), then the DMA transaction has transitioned from the TRANSFER state to the TRANSFER_COMPLETED state. The DpcFunction routine begins the post-transfer phase of the DMA transaction.

Step 324: A call to the DmaTransactionGetBytesTransferred method of the DMA transaction object gets the final DMA transfer byte count to be used for completing the Write Request.

Step 326: In the example of FIG. 3, the DMA transaction object is destroyed by calling DmaTransactionDelete. (See step 100 of FIG. 1.)

FIGS. 4 through 10 present variations on the basic scheme portrayed in FIGS. 1 and 3. In FIG. 4, a DMA transaction is initiated. The working environment is the device manager's Read- or Write-Request dispatch function where a REQUEST handle, representing the Request, is passed as a parameter.

Step 300: DmaTransactionCreate creates an empty DMA transaction object.

Step 302: DmaTransactiornnitializeUsingRequest initializes the, DMA transaction. The operating parameters for the DMA transaction are captured by querying the Request and its underlying IRP (Input/output Request Packet).

Step 304: DmaTransactionExecute validates the DMA transaction (e.g., has it been successfully initialized?) and then calls BuildScatterGatherList.

Step 306: From this point on, the processing is the same as described in FIG. 3.

FIG. 5 shows a variation on FIG. 4 in which the DMA transaction object is updated to operate with a MaximumLength other than the default set when the DMA enabler object was created. The MaximumLength value controls the maximum byte count per DMA transfer for this DMA transaction. The new MaximumLength is less than or equal to the DMA enabler's MaximumLength.

Steps 300 and 302: Same as for FIG. 4.

Step 500: DmaTransactionSetMaximumLength sets the MaximumLength for this particular DMA request.

Step 304: From this point on, the processing is the same as described in FIG. 3.

FIG. 6 illustrates how a device manager itself can initiate a DMA transaction without the transaction being coupled with a Request or with an external IRP. This is also useful where finer control over the DMLA transaction parameters is needed, such as when manipulating the starting Virtual Address or Length.

Step 300: DmaTransactionCreate creates an empty DMA transaction object.

Step 302: DmaTransactionInitialize initializes the DMA transaction. The operating parameters for the DMA transaction are passed as parameters, rather than being taken from a Request.

Step 304: From this point on, the processing is the same as described in FIG. 3.

FIG. 7 shows how a device manager notifies the DMA transaction object of a just completed DMA transfer. This diagram is a subsection of FIG. 2. In the example of FIG. 7, it is assumed the device hardware does not report the length (byte count) of the DMA transfer. The DMA transaction object assumes that the transferred length is the length passed to the device manager's PFN_PROGRAM_DMA callback function.

Step 700: The device generates an interrupt to signal the completion of a DMA transfer.

Step 702: The device manager's ISR function determines that it owns the interrupt and then schedules the DPC function.

Step 704: The device manager's DPC function determines which DMA transaction matches the just completed DMA transfer. It then calls DmaTransactionDmaCompleted to communicate this event to the DMA transaction object.

Step 706: In response, the DMA transaction object determines whether (a) more processing is needed for this DMA transaction or (b) the DMA transaction has transferred all the data. DmaTransactionDmaCompleted returns TRUE if the DMA transaction transitioned from the TRANSFER state to the TRANSFER_COMPLETED state. (See FIG. 1.) FALSE means that more DMA transfers are needed to complete the DMA transaction. The DMA transaction states are also indicated by the returned status: MORE_PROCESSING_REQUIRED means there has been no state change (TRANSFER state), while a non-MORE_PROCESSING_REQUIRED means that there has been a transition to the TRANSFER_COMPLETED state.

Step 708: In response to a completion indicator, the device manager gets the final transfer length from the DMA transaction.

Step 710: The DMA transaction is deleted. This flushes the underlying map registers and caches. If the DMA transaction was initialized via DmaTransactionInitializeUsingRequest, then the reference on the Request is dropped.

FIG. 8 is a variation on FIG. 7 where the device provides the actual number of bytes transferred in the DMA transaction.

Steps 700 and 702: Same as for FIG. 7.

Step 704: The device manager's DPC function determine which DMA transaction matches the just completed DMA transfer. The device manager queries the device for the transferred length and then calls DmaTransactionDmaCompletedWithLength to communicate this event to the DMA transaction object.

Step 706: In response, the DMA transaction object uses the transferred length to determine whether more processing is needed for this DMA transaction.

Step 708: If the DMA transfer is complete, then the device manager gets the final transfer length from the DMA transaction object.

Step 710: Same as for FIG. 7.

FIG. 9 is a variation on FIG. 8 in which the device manager detects a DMA under-fill condition and notifies the DMA transaction object of this terminal event. All other aspects of this scenario are as shown in FIG. 8.

Steps 700 and 702: Same as for FIG. 7.

Step 900: The device manager determines that the device reported the DMA transferred length as a final length. To report this terminal event, the device manager calls DmaTransactionDmaCompletedFinal.

Step 706: In response, the DMA transaction object uses the transferred length to determine whether more processing is needed for this DMA transaction. In this case, the DMA transaction object returns FALSE and a non-MORE_PROCESSING_REQUIRED status, thus indicating that the device manager should perform post-transfer processing for this DMA Request.

Step 708: In response to the non-MORE_PROCESSING_REQUIRED status, the device manager gets the final transfer length from the DMA transaction object. The transferred length value includes the final transferred length.

Step 710: Same as for FIG. 7.

FIG. 10 presents a method for handling low-resource conditions. These conditions are usually experienced as the inability of a device manager to dynamically acquire memory, especially at a critical juncture such as paging. The method of FIG. 10 allows the device manager to continue to make “forward progress” under low-resource conditions. “Reserved” DMA transaction objects may be allocated when resources are not scarce, usually during device manager initialization. Later, when a low-resource condition arises, the “reserved” DMA transactions are brought out of reserve and initialized.

Step 1000: During AddDevice or StartDevice, one or more DMA transaction objects are created and designated as “reserved.”

Step 1002: When a low-resource condition occurs, the device manager pulls a DMA transaction object from its reserve pool and initializes it. The initialization function, DmaTransactionInitialize[UsingRequest], reinitializes the DMA transaction to a reset state prior to capturing the operating parameters.

Step 1004: After processing, the DMA transaction is released by calling DmaTransactionRelease. This function causes the DMA transaction to flush any buffers. In contrast to ObjectDelete, the DMA transaction may be placed back in the reserve pool for later reuse.

(Not shown in FIG. 10) Eventually, the reserved DMA transaction objects in the pool are freed by calling ObjectDelete. DmaEnablerDelete checks to insure that no DMA transactions-are still associated with the DMA enabler.

The following is an exemplary implementation of the fuctionality described above in relation to FIGS. 1 through 10. This implementation is meant purely as a teaching aid illustrating some concepts of the present invention and is not meant to limit the scope of that invention in any way.

DmaEnablerCreate

STATUS DmaEnablerCreate ( IN DEVICE Device, IN DMA_OBJECT_CONFIG * DmaConfig, IN OBJECT_ATTRIBUTES * Attributes OPTIONAL, OUT DMAENABLER * DmaEnabler );

-   -   DmaEnablerCreate creates a DMA enabler instance from which to         stage subsequent DMA operations and returns a DMAENABLER handle.         Parameters:     -   Device         -   Specifies the DEVICE handle to be associated with the DMA             enabler.     -   DmaConfig         -   Specifies a pointer to a DMA_ENABLER_CONFIG structure. This             DMA configuration structure is initialized via             DMA_ENABLER_CONFIG_INIT.     -   Attributes         -   Specifies the generic object attributes associated with the             DMA enabler.         -   These attributes include context size and the object's             destroy callback function.     -   DmaEnabler         -   Points to a DMAENABLER which will receive the created DMA             enabler handle.             Returned Value:     -   DmaEnablerCreate returns STATUS_SUCCESS when a new DMA enabler         has been successfully created. Some possible failure status         values are:         -   STATUS_INVALID_PARAMETER—An invalid parameter was detected.         -   STATUS_INSUFFICIENT_RESOURCES—There was not enough memory to             construct a new DMA enabler.             Comments:     -   This function is called at IRQL=PASSIVE_LEVEL.     -   Prior to calling DmaEnablerCreate, the device manager sets its         alignment requirement via the DeviceSetAligrinentRequirement         function.         See Also:     -   ObjectReference, ObjectSetDestroyCallback, DmaEnablerDelete

DMA_ENABLER_CONFIG_INIT

VOID DMA_ENABLER_CONFIG_INIT ( IN DMA_ENABLER_CONFIG * DmaConfig, IN DMA_PROFILE Profile, IN size_t MaximumLength );

-   -   DMA_ENABLER_CONFIG_INIT initializes the DMA enabler         configuration structure for subsequent use by DmaEnablerCreate.         Parameters:

Profile Specifies the DMA operations profile the DMA enabler will be configured to support. typedef enum_DMA_PROFILE { DmaProfilePacket = 0, DmaProfileScatterGather, DmaProfilePacket64, DmaProfileScatterGather64, DmaProfileScatterGatherDuplex, DmaProfileScatterGather64Duplex, } DMA_PROFILE; Note: Some duplex-type profiles, such as DmaProfilePacketDuplex or DmaProfilePacket64Duplex, are not supported for packet mode operations.

-   -   MaximumLength         -   Specifies the maximum DMA transfer, in bytes, that can be             handled in a single DMA operation. Good-citizen values             should be less than 65536 (0x10000). This good-citizen value             is based on the current upper limit of 16 map registers             imposed by current HALs (Hardware Abstraction Layers).         -   Note: On some OS levels, the recommended limit of 16 map             register may be relaxed. But if the drive is to target             multiple OS levels, then this value may need to be             restricted to the proposed value cited above.             Returned Value:     -   None         Comments:     -   This function is called at IRQL=PASSIVE_LEVEL.     -   Prior to calling DmaEnablerCreate, the device manager sets its         alignment requirement via the DeviceSetAlignmentRequirement.         See Also:     -   ObjectReference, ObjectSetDestroyCallback, DmaEnablerDelete

DmaEnablerGetMaximumLength

size_t DmaEnablerGetMaximumLength (   IN DMAENABLER DmaEnabler );

-   -   DmaEnablerGetAaximumLength gets the current MaximumLength         setting in the referenced DMA enabler.         Parameters:     -   DmaEnabler         -   The DmaEnabler handle which was returned from a successful             DmaEnablerCreate. This function does not affect the state of             the DMA enabler.             Returned Value:     -   The returned value is the maximum length of a DMA transfer in         bytes. This value is the same as the maximum length specified in         the DmaEnablerCreate function call.         Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.

DmaEnablerSetMaximumScatterGatherElements

VOID DmaEnablerSetMaximumScatterGatherElements ( IN DMAENABLER DmaEnabler IN size_t MaximumElements ); DmaEnablerSetMaximumScatterGatherElements sets the maximum number of SCATTER_GATHER_ELEMENTS which the device manager supports. Parameters:

-   -   DmaEnabler         -   The DmaEnabler handle returned from a successful             DmaEnablerCreate.     -   MaximumElements         -   MaximumElements is the maximum number of scatter/gather             elements which the device manager supports. This function is             optional, and if not called, then the DMA enabler implicitly             uses a default value of DMA_ENABLER_UNLIMITED_FRAGMENTS to             indicate no limitation.             Returned Value:     -   None         Comments:     -   This function is called at IRQL=PASSIVE_LEVEL.     -   The DmaEnablerSetMaximumScatterGatherElements function is used         during device initialization after a successful call to         DmaEnablerCreate.         See Also:     -   DmaEnablerCreate, DmaEnablerGetMaximumScatterGatherElements

DmaEnablerGetMaximumScatterGatherElements

size_t DmaEnablerGetMaximumScatterGatherElements (   IN DMAENABLER DmaEnabler ); DmaEnablerGetMaximumScatterGatherElements gets the maximum number of SCATTER_GATHER_ELEMENTS which the device manager supports. Parameters:

-   -   DmaEnabler         -   The DmaEnabler handle returned from a successful             DmaEnablerCreate.             Returned Value:     -   The returned value is the maximum number of scatter/gather         elements which the device manager supports. The default         “unlimited” value is indicated by a value of         DMA_ENABLER_UNLIMITED_FRAGMENTS.         Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   DmaEnablerCreate, DmaEnablerSetMaximumScatterGatherElements

DmaTransactionCreate

STATUS DmaTransactionCreate ( IN DMAENABLER DmaEnabler, IN OBJECT_ATTRIBUTES * Attributes OPTIONAL, OUT DMATRANSACTION * DmaTransactionHandle )

-   -   DmaTransactionCreate creates a new DMA transaction instance. The         returned DMA transaction is initialized with         DmaTransactionInitialize[UsingRequest] before it is executed via         DmaTransactionExecute. The separation of the create action from         the initialize action allows the device manager developer to         reserve DMA Request objects for low-resource conditions.         Parameters:     -   DmaEnabler         -   The DMAENABLER handle returned from a successful             DmaEnablerCreate.     -   Attributes         -   Specifies the generic object attributes associated with the             DMA transaction.         -   These attributes include context size and the object's             destroy callback function.     -   DmaTransactionHandle         -   This is the returned DMA transaction handle which will be             used for this life of this DMA Request. It represents this             unique DMA transaction. When this DMA transaction is             complete, ObjectDelete or DmaTransactionRelease is called.             Returned Value:     -   DmaTransactionCreate returns STATUS_SUCCESS when a new DMA         transaction object is successfully created. Possible failure         return status values are:         -   STATUS_INVALID_PARAMETER—An invalid parameter was detected.         -   STATUS_INSUFFICIENT_RESOURCES—There was not enough memory to             construct a new DMA transaction instance.             Comments:     -   This function may be called at IRQL=PASSIVE_LEVEL.         See Also:     -   DmaTransactionExecute, ObjectDelete, DmaTransactionDmaCompleted,         DmaTransactionRelease

DmaTransactionInitializeUsingRequest

STATUS DmaTransactionInitializeUsingRequest ( IN DMATRANSACTION DmaTransaction, IN REQUEST Request, IN PFN_PROGRAM_DMA EvtProgramDmaFunction, IN DMA_DIRECTION DmaDirection )

-   -   DmaTransactionInitializeUsingRequest initializes (or         reinitializes) a DMA transaction instance. This function does         not start a DMA operation. Rather it captures the Request         parameters in the DMA transaction instance. A subsequent call to         DmaTransactionExecute initiates the first (and perhaps only) DMA         transfer for this DMA transaction.         DmaTransactionInitializeUsingRequest is typically called from a         device manager's input/output Dispatch routine.         Parameters     -   DmaTransaction         -   This is a DMA Transaction handle returned from             DmaTransactionCreate.     -   Request         -   The Request parameter is the input/output queue Request             handle. The Request parameter is normally a parameter on the             device manager's Dispatch (IRP_MJ_WRITE, for example) or             StartIo routine. This Request is coupled with the DMA             Request.     -   EvtProgramnDmaFunction         -   This is the device-specific function that focuses on device             specifics of programming a DMA operation. The prototype for             this callback is shown below. If the device manager's             ProgramDmaFunction succeeds in starting the DMA operation,             the TRUE is returned, otherwise FALSE.

typedef BOOLEAN (*PFN_PPROGRAM_DMA) (   IN DEVICE Device,   IN PVOID Context,   IN DMA_DIRECTION Direction,   IN PSCATTER_GATHER_LIST SgList );

-   -   DmaDirection         -   DmaDirection is an enumeration with two values, representing             the two possible directions of the DMA transfer.

typedef enum_DMA_DIRECTION {   DmaDirectionReadFromDevice = FALSE,   DmaDirectionWriteToDevice = TRUE, } DMA_DIRECTION; Returned Value:

-   -   DmaTransactionInitializeUsingRequest returns STATUS_SUCCESS when         a DMA transaction instance is successfully initialized. Possible         failure return status values are:         -   STATUS_INVALID_PARAMETER—An invalid parameter was detected.         -   STATUS_INVALID_DEVICE_REQUEST—The input/output queue Request             contains an invalid MDL.             Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   DmaTransactionCreate, DmaTransactionExecute, ObjectDelete,         DmaTransactionDmaCompleted

DmaTransactionInitialize

STATUS DmaTransactionInitialize (   IN DMATRANSACTION DmaTransaction,   IN PFN_PROGRAM_DMA EvtProgramDmaFunction,   IN DMA_DIRECTION DmaDirection,   IN PMDL Mdl,   IN PVOID Offset,   IN size_t Length )

-   -   DmaTransactionInitialize initializes (or reinitializes) a DMA         transaction from direct, lower-level parameters. It may be used         when the device manager wishes to perform a DMA operation but         does not have a Request instance. This contrasts with         DmaTransactionInitializeUsingRequest which internally extracts         similar parameters from the Request.         Parameters:     -   DmaTransaction         -   This is the DMA transaction handle returned from             DmaTransactionCreate.     -   EvtProgramDmaFunction         -   This function focuses on device specifics of programming a             DMA operation. The prototype for this callback is shown             below. If the device manager's PrograniDmaFunction succeeds             in starting a DMA operation, then TRUE is returned,             otherwise FALSE.

typedef BOOLEAN (*PFN_PPROGRAM_DMA) (   IN PVOID Context,   IN DMA_DIRECTION Direction,   IN PSCATTER_GATHER_LIST SgList );

-   -   DmaDirection         -   DmaDirection is an enumeration with two values, representing             the two possible directions of the DMA transfer.

typedef enum_DMA_DIRECTION {   DmaDirectionReadFromDevice = FALSE,   DmaDirectionWriteToDevice = TRUE, } DMA_DIRECTION;

-   -   Mdl         -   This is a pointer to a filled in MDL structure.     -   Offset         -   This is an offset to where the DMA transaction is to begin             DMA operations. Typically it is the top of the buffer to be             transferred, although it may be adjusted to any valid offset             within that buffer.     -   Length         -   This is the length of the buffer to be transferred. This             should be adjusted if an Offset other than the starting             offset is specified.             Returned Value:     -   DmaTransactionInitialize returns STATUS_SUCCESS when a new DMA         transaction is successfully initialized. A possible failure         return status value is:         -   STATUS_INVALID_PARAMETER—An invalid parameter was detected.             Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   DmaTransactionCreate, DmaTransactionExecute, ObjectDelete,         DmaTransactionDmaCompleted

DmaTransactionExecute

STATUS DmaTransactionExecute (   IN DMATRANSACTION DmaTransaction,   IN PVOID Context )

-   -   DmaTransactionExecute executes a DMA transaction. This function         stages the setup for the first DMA operation and calls the         device manager's PFN_PROGRAM_DMA function. Typically this         function is called from within the device manager's Dispatch         routine after creating and initializing the DMA transaction.         Because DmaTransactionExecute initiates DMA transaction         processing, there should be only one call to         DmaTransactionExecute per DMA transaction instance. Subsequent         calls to DmaTransactionExecute would fail but would not abort         the DMA transaction.         Parameters:     -   DmaTransaction         -   DmaTransaction is the handle returned from             DmaTransactionCreate and identifies the specific DMA             transaction to be processed.     -   Context         -   This is the device manager's determined values which are             presented as the Context when the device manager's             PFN_PROGRAM_DMA callback is executed.             Returned Value:     -   DmaTransactionExecute returns STATUS_SUCCESS when the DMA         transaction is successfully initiated. Possible failure return         values are:         -   STATUS_INVALID_PARAMETER—An invalid parameter was detected.         -   STATUS_INVALID_DEVICE_REQUEST—A subsequent (non-initial)             call was made to DmaTransactionExecute.             Comments:     -   This function can be called at IRQL<=DISPATCH_LEVEL.     -   If the caller supplies a Context value of a pointer type, then         the area to which it is pointing should be available within the         PFN_PROGRAM_DMA context (which will be at DISPATCH_LEVEL IRQL.)         If possible, it is good to use an object context, as this         satisfies these preconditions.         See Also:     -   DmaTransactionCreate, ObjectDelete, DmaTransactionDmaCompleted

DmaTransactionRelease

STATUS DmaTransactionRelease (   IN DMATRANSACTION   DmaTransaction )

-   -   DmaTransactionRelease terminates a DMA transaction but does not         delete the DMA transaction instance. Upon completion of this         function call, all transfer buffers are flushed and all         DmaEnabler resources acquired for this transaction are released.         Parameters:     -   DmaTransaction         -   DmaTransaction is the handle returned from             DmaTransactionCreate and identifies the specific DMA             transaction to be processed.             Returned Value:     -   DmaTransactionRelease returns STATUS_SUCCESS when the DMA         transaction has been successfully released. A possible failure         return status is:         -   STATUS_INVALID_PARAMETER—An invalid parameter was detected.             Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   DmaTransactionCreate, DmaTransactionExecute,         DmaTransactionDmaCompleted

DmaTransactionDmaCompleted

BOOLEAN DmaTransactionDmaCompleted (   IN DMATRANSACTION DmaTransaction,   OUT STATUS * Status )

-   -   DmaTransactionDmaCompleted notifies a DMA transaction object         that the DMA transfer operation (started via the device         manager's PFN_PROGRAM_DMA function) is complete.         DmaTransactionDmaCompleted is typically called from the device         manager's DPC routine in response to detecting the completion of         a DMA transfer operation. The call to DmaTransactionDmaCompleted         allows the DMA transaction object to continue processing. The         returned Boolean indicates whether the DMA transaction requires         more processing (TRUE). FALSE does not mean that the data were         successfully transferred; the updated Status parameter indicates         if the DMA transaction was successful. In any case, there will         be no further DMA transfers for this DMA transaction.         Parameters:     -   DmaTransaction         -   DmaTransaction is the handle returned from             DmaTransactionCreate and identifies the specific DMA             transaction to be processed.     -   Status         -   A pointer to a STATUS. STATUS is updated with the             DmaTransactionDmaCompleted status (see comments below).             Returned Value:     -   If the DMA transaction needs to do more DMA transfers in order         to complete the DMA transaction, then TRUE is returned and         Status is set to STATUS_MORE_PROCESSING_REQUIRED.     -   A return value of FALSE indicates that the DMA transaction         transitioned from the TRANSFER state to the TRANSFER_COMPLETED         state. Status indicates whether the data were transferred         successfully (STATUS_SUCCESS).         Comments:     -   This function may be called at IRQL=DISPATCH_LEVEL.     -   It is the device manager's responsibility to determine which DMA         transaction has completed.     -   The updated status value falls into one of three categories:         -   STATUS_SUCCESS—The transfer is successful. The device             manager should complete the input/output queue Request.         -   STATUS_MORE_PROCESSING_REQUIRED—The transaction contains             more DMA operations, and the next DMA operation has been             scheduled to the device manager's PFN_PROGRAM_DMA callback             function. For simple device managers, a typically response             to this status may be to clear the interrupt and return from             the DPC routine. Subsequent interrupts and calls to             DmaTransactionDmaComplete will eventually signal the             completion of the DMA transaction.         -   STATUS_<errorcode>—This represents an error condition in the             transaction. The device manager should call             DmaTransactionDelete and then RequestCompleteEx to complete             the input/output queue Request with the returned status.             See Also:     -   DmaTransactionCreate, DmaTransactionExecute,         DmaTransactionDelete

DmaTransactionDmaCompletedWithLength

-   -   BOOLEAN     -   DmaTransactionDmaCompletedWithLength

BOOLEAN DmaTransactionDmaCompletedWithLength (   IN DMATRANSACTION DmaTransaction,   IN size_t TransferredLength,   OUT STATUS * Status )

-   -   DmaTransactionDmaCompletedWithLength notifies a DMA transaction         that the DMA operation (started in the device manager's         PFN_PROGRAM_DMA function) is complete and that the device has         provided the DMA transfer length (byte count).     -   DmaTransactionDmaCompletedWithLength is typically called from         the device manager's DPC routine in response to detecting the         completion of a DMA transfer operation. The call to         DmaTransactionDmaCompletedWithLength allows the DMA transaction         object to continue processing. The returned Boolean indicates         whether the DMA transaction requires more processing (TRUE).         FALSE does not mean that the data were successfully transferred;         the updated Status parameter indicates if the DMA transaction         was successful. In any case, there will be no further DMA         transfers for this DMA transaction.         Parameters:     -   DmaTransaction         -   DmaTransaction is the handle returned from             DmaTransactionCreate and identifies the specific DMA             transaction to be processed.     -   TransferredLength         -   The device-provided DMA transfer length (i.e., the byte             count).     -   Status         -   A pointer to a STATUS. STATUS is updated with the             DmaTransactionDmaCompletedWithLength status (see comments             below).             Returned Value:     -   If the DMA transaction needs to do more DMA transfers, then TRUE         is returned, and Status is set to         STATUS_MORE_PROCESSING_REQUIRED.     -   A return value of FALSE indicates that the DMA transaction has         transitioned from the TRANSFER state to the TRANSFER_COMPLETED         state. Status indicates whether the data were transferred         successfully (STATUS_SUCCESS).         Comments:     -   This function may be called at IRQL=DISPATCH_LEVEL.     -   It is the device manager's responsibility to determine which DMA         transaction has completed.     -   The updated status value falls into one of three categories:         -   STATUS_SUCCESS—The transfer is successful. The device             manager should complete the Request.         -   STATUS_MORE_PROCESSING REQUIRED—The transaction contains             more DMA operations, and the next DMA operation has been             scheduled to the device manager's PFN_PROGRAM DMA callback             function. For simple device managers, a typically response             to this status may be to clear the interrupt and return from             the DPC routine. Subsequent interrupts and calls to             DmaTransactionDmaComplete will eventually signal the             completion of the DMA transaction.         -   STATUS_<errorcode>—This represents an error condition in the             transaction. The device manager should call ObjectDelete and             then RequestCompleteEx to complete the input/output queue             Request with the returned status.             See Also:     -   DmaTransactionCreate, DmaTransactionExecute, ObjectDelete

DmaTransactionDmaCompletedFinal

BOOLEAN DmaTransactionDmaCompletedFinal (   IN DMATRANSACTION DmaTransaction   IN size_t FinalTransferredLength,   OUT STATUS * Status )

-   -   DmaTransactionDmaCompletedFinal notifies a DMA transaction that         the DMA operation started in the device manager's         PFN_PROGRAM_DMA function is complete and that the device         provided the DMA transferred length (byte count).         DmaTransactionDmaCompletedFinal is typically called from the         device manager's DPC routine in response to detecting the         completion of a DMA operation. It allows the DMA transaction         object to continue processing the DMA transaction. This function         causes the DMA transaction to transition from the TRANSFER state         to TRANSFER_COMPLETED.         Parameters:     -   DmaTransaction         -   DmaTransaction is the handle returned from             DmaTransactionCreate and identifies the specific DMA             transaction to be processed.     -   FinalTransferredLength         -   The device-provided DMA transfer length (i.e., byte count).     -   Status         -   A pointer to a STATUS. STATUS is updated with the             DmaTransactionDmaCompletedFinal status (see comments below).             Returned Value:     -   FALSE is always returned indicating that there will be no         further DMA transfers.         Comments:     -   This function can be called at IRQL=DISPATCH_LEVEL.     -   The FALSE return value (always returned) facilitates         common-status-processing code patterns involving the functions         DmaTransactionDmaCompletedWithLength and         DmaTransactionDmaCompletedFinal.         See Also:     -   DmaTransactionCreate, DmaTransactionExecute, ObjectDelete

DmaTransactionSetMaximumLength

VOID DmaTransactionSetMaximumLength (   IN DMATRANSACTION DmaTransaction   IN size_t MaximumLength )

-   -   DmaTransactionSetMaximumLength overrides the default         MaximumLength value only for only this one DMA transaction         instance. The DMA transaction instance was created with a         default value derived from the DMA enabler. The effective DMA         transaction MaximumLength is MIN(DMA enabler's MaximumLength,         MaximumLength).         Parameters:     -   DmaTransaction         -   DmaTransaction is the handle returned from             DmaTransactionCreate and identifies the specific DMA             transaction to be processed.     -   MaximumLength         -   MaximumLength should be less than or equal to the DMA             enabler's MaximumLength value.         -   Note: This is a Set property function, that is, no status is             returned if this parameter is greater than the default             value.             Returned Value:     -   None         Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   DmaTransactionCreate, DmaTransactionInitialize,     -   DmaTransactionInitializeUsingRequest, DmaTransactionExecute,         ObjectDelete

DmaTransactionGetBytesTransferred

size_t DmaTransactionGetBytesTransferred (   IN DMATRANSACTION  DmaTransaction )

-   -   DmaTransactionGetBytesTransferred is called to get the number of         bytes transferred by this DMA transaction. This function is         typically used to get the final transferred byte count to be         returned in the RequestCompleteEx function call.         Parameters:     -   DmaTransaction         -   DmaTransaction is the handle returned from             DmaTransactionCreate and identifies the specific DMA             transaction to be processed.             Returned Value:     -   The current number of bytes transferred by this DMA transaction.         Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   DmaTransactionCreate, DmaTransactionExecute, ObjectDelete

DmaTransactionGetRequest

REQUEST DmaTransactionGetRequest (   IN DMATRANSACTION   DmaTransaction )

-   -   DmaTransactionGetRequest is called to get the REQUEST handle         associated with the specified DMA transaction.         Parameters:     -   DmaTransaction         -   A DmaTransaction handle returned from DmaTransactionCreate.             Returned Value:     -   The handle to the associated REQUEST Request for this DMA         Transaction. This is the Request parameter value of the         DmaTransactionIntializeUsingRequest function.     -   A NULL return indicates an error condition or that the DMA         transaction was created via DmaTransactionnitialize, which does         not associate the DMA transaction with a REQUEST handle.         Comments:     -   This function should be used with         DmaTransactionnitializeUsingRequest, not with         DmaTransactionInitialize.     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   DmaTransactionCreate, DmaTransactionInitializeUsingRequest

DmaTransactionGetCurrentDmaTransferLength

size_t DmaTransactionGetCurrentDmaTransferLength (   IN DMATRANSACTION   DmaTransaction )

-   -   DmaTransactionGetCurrentDmaTransferLength gets the current DMA         transfer size.     -   This function is typically called from the device manager's DPC         routine.         Parameters:     -   DmaTransaction         -   The DmaTransaction handle returned from             DmaTransactionCreate.             Returned Value:     -   The length of the current DMA transfer. If this function is         called while the DMA transaction in progress (that is, its state         is TRANSFER), then the return value is the actual number of         bytes successfully transferred at that time. If called after the         state transition to TRANSFER_COMPLETED with a successful status,         then the return value is the final transferred byte count.         Comments:     -   This function is typically used for devices which report         residual transfer lengths (that is, the byte count for         yet-to-be-transferred data). By subtracting the value returned         by DmaTransactionGetCurrentDmaTransferLength from the         device-reported residual byte count, the actual transfer length         is derived. This could then be reported via         DmaTransactionDmaCompletedWithLength.     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   DmaTransactionCreate, DmaTransactionDmaCompletedWithLength

DmaTransactionGetDevice

DEVICE DmaTransactionGetDevice (   IN DMATRANSACTION   DmaTransaction )

-   -   DmaTransactionGetDevice is called to get the DEVICE handle         associated with the specified DMA transaction.         Parameters:     -   DmaTransaction         -   The DmaTransaction handle returned from             DmaTransactionCreate.             Returned Value:     -   The handle to the associated Device for this DMA transaction.         This is the Device parameter value of DmaTransactionCreate.         Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   DmaTransactionCreate

CommonBufferCreate

STATUS CommonBufferCreate (   IN DMAENABLER DmaEnabler,   IN size_t Length,   IN POBJECT_ATTRIBUTES Attributes OPTIONAL,   OUT COMMONBUFFER * CommonBuffer )

-   -   CommonBufferCreate allocates memory and maps it so that it is         simultaneously accessible from both the processor and from a         device for DMA operations. The returned COMMONBUFFER handle is         used on subsequent CommonBuffer API calls, such as         CommonBufferGetAlignedVirtualAddress, to reference this         CommonBuffer object.         Parameters:     -   DmaEnabler         -   A DMA enabler handle returned from a successful             DmaEnablerCreate.     -   Length         -   This is the size of the allocated memory in bytes.     -   Attributes         -   Specifies the generic object attributes associated with the             CommonBijffer object. These attributes include context size             and the object's destroy callback function. It may be NULL             if no context area is desired.     -   CommonBufferHandle         -   This is a pointer to a COMMONBUFFER variable which receives             the new CommonBuffer object's handle.             Returned Value:     -   CommonBufferCreate returns STATUS_SUCCESS to indicate that the         requested common buffer memory has been allocated.         Comments:     -   This function must be called at IRQL=PASSIVE_LEVEL.     -   The device manager sets its alignment requirement, via the         function DeviceSetAlignmentRequirement, prior to calling this         function. This is typically done in the AddDevice or StartDevice         routines when the device is initialized.     -   Note: There is no cache option for this function as in         AllocateCommonBuffer. This is because all platforms implement         cache flushing per the ×86 HAL model. In other words, the         buffers are allocated as cached by the HAL; the         AllocateCommonBuffer cache options are effectively ignored.     -   Below is a snippet of code which shows the general pattern of         COMMONBUFFER objects.

//================== Create a Common Buffer =============== DevExt->CommonBufferSize = sizeof(COMMON_BUFFER_STRUCT); status = CommonBufferCreate(DevExt->DmaEnabler,  DevExt->CommonBufferSize, NO_ATTRIBUTES,  &DevExt->CommonBuffer); if(status == STATUS_SUCCESS) {  DevExt->CommonBufferBaseVA =   CommonBufferGetAlignedVirtualAddress(DevExt->CommonBuffer);  DevExt->CommonBufferBaseLA =   CommonBufferGetAlignedLogicalAddress(DevExt->   CommonBuffer); } //================== Destroy a Common Buffer =============== if(DevExt->CommonBuffer) {  CommonBufferDelete(DevExt->CommonBuffer);  DevExt->CommonBuffer = NULL; } See Also:

-   -   CommonBufferDelete

CommonBufferGetAlignedVirtualAddress

PVOID CommonBufferGetAlignedVirtualAddress (   IN COMMONBUFFER CommonBuffer )

-   -   CommonBufferGetAlignedVirtualAddress returns the aligned virtual         address for a CommonBuffer object. The device manager does not         need to adjust the virtual address to the CommonBuffer memory         itself, but rather allows this function to manage alignment         issues.         Parameters:     -   CommonBufferHandle         -   A COMMONBUFFER handle returned from a successful call to             CornmonBufferCreate.             Returned Value:     -   A virtual address pointer which is properly aligned per the         device's alignment requirements and per the platform's alignment         requirements.         Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   CommonBufferCreate, CommonBufferGetAlignedLogicalAddress

CommonBufferGetAlignedLogicalAddress

PHYSICAL_ADDRESS CommonBufferGetAlignedLogicalAddress (   IN COMMONBUFFER CommonBuffer )

-   -   CommonBufferGetAlignedLogicalAddress returns the aligned logical         address for; a CommonBuffer object. The device manager does not         need to adjust the logical address to the CommonBuffer memory         itself, but rather allows this function to manage alignment         issues.         Parameters:     -   CommonBufferHandle         -   A COMMONBUFFER handle returned from a successful call to             CommonBufferCreate.             Returned Value:     -   A PHYSICAL_ADDRESS value which is properly aligned per the         device's alignment requirement and per the platform's alignment         requirements.         Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   CommonBufferCreate, CommonBufferGetAlignedVirtualAddress

CommonBufferGetLength

size_t CommonBufferGetLength (   IN COMMONBUFFER CommonBuffer )

-   -   CommonBufferGetLength returns the length of the buffer         associated with the CommonBuffer object. This is the same length         specified for the creation of the CommonBuffer object.         Parameters:     -   CommonBufferHandle         -   A COMMONBUFFER handle returned from a successful call to             CommonBufferCreate.             Returned Value:     -   The length value used to create the CommonBuffer object.         Comments:     -   This function may be called at IRQL<=DISPATCH_LEVEL.         See Also:     -   CommonBufferCreate

In view of the many possible embodiments to which the principles of the present invention may be applied, it should be recognized that the embodiments described herein with respect to the drawing figures are meant to be illustrative only and should not be taken as limiting the scope of the invention. Those of skill in the art will recognize that some implementation details, such as the details of the APIs, are determined by specific situations. Although the environment of the invention is described in terms of software modules or components, some processes may be equivalently performed by hardware components. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof. 

1. In a computing environment, a method for structuring at least a first programmed input/output (PIO) transaction, the method comprising: employing a processor executing computer-executable code stored in memory to implement the following acts: constructing a first PIO transaction object upon a request for a first PIO transaction, the construction of the first PIO transaction object comprises referencing a PIO enabler object, wherein the enabler object captures general PIO operational parameters and manages underlying operating system objects; initializing data in the first PIO transaction object specific to the transaction request; and processing the first PIO transaction to completion in conjunction with transitioning the first PIO transaction object through processing states, wherein initializing data in the first PIO transaction object comprises initializing data selected from a set including: the first PIO transaction, a direction of the first PIO transaction, an offset into a buffer containing data to be transferred for the first PIO transaction, or a length of data to be transferred for the first PIO transaction.
 2. The method of claim 1, the method runs in a device manager.
 3. The method of claim 2, the device manager is a kernel-mode device driver.
 4. The method of claim 1, transitioning the first PIO transaction object comprises calling an application program interface (API) of the first PIO transaction object.
 5. The method of claim 4, the API of the first PIO transaction object is selected from a set including: PIO Transaction Execute, PIO Transaction Completed, PIO Transaction Get Bytes Transferred, or PIO Transaction Release.
 6. The method of claim 1, further comprising: receiving an input/output request for the first PIO transaction from an operating system.
 7. The method of claim 1, further comprising: constructing the PIO enabler object prior to constructing the first PIO transaction object; and initializing data in the PIO enabler object.
 8. The method of claim 7, initializing data in the PIO enabler object comprises selecting one of a plurality of profiles, wherein a profile is associated with a device requesting the first PIO transaction.
 9. The method of claim 1, further comprising: providing status of the first PIO transaction, the status comprising an amount of data transferred in the first PIO transaction.
 10. The method of claim 1, further comprising: deleting the first PIO transaction object.
 11. The method of claim 1, a second PIO transaction is structured, and structuring the second PIO transaction comprises: re-initializing data in the first PIO transaction object; and processing the second PIO transaction to completion in conjunction with transitioning the first PIO transaction object through processing states.
 12. The method of claim 1, a second PIO transaction is structured, and structuring the second PIO transaction comprises: constructing a second PIO transaction object; initializing data in the second PIO transaction object; and processing the second PIO transaction to completion in conjunction with transitioning the second PIO transaction object through processing states.
 13. A computer-readable medium comprising: employing a processor executing computer-executable instructions stored on the computer-readable storage medium to implement the following acts: dispatching a programmed input/output (PIO) work request for a PIO transaction from a device manager; constructing a PIO transaction object representing the PIO work request by referencing a PIO enabler object, the enabler object is constructed prior to the construction of the PIO transaction object, wherein the enabler object captures general PIO operational parameters and manages underlying operating system objects; initializing data particular to the work request in the PIO transaction object; and processing the PIO transaction to completion in conjunction with transitioning the PIO transaction object through processing states, wherein the transitioning comprises calling an application program interface (API) of the PIO transaction object, the API of the PIO transaction object being selected from a set including: PIO Transaction Execute, PIO Transaction Completed, PIO Transaction Get Bytes Transferred, or PIO Transaction Release.
 14. A system for structuring at least a first programmed input/output (PIO) transaction in a computing environment, the system comprising: a memory; and a processor, operatively coupled to the memory, the processor executing computer-executable instructions to effect the following: an operating system configured for sending an input/output request for the first PIO transaction to a device manager; and a device manager configured for: receiving the input/output request, constructing a first PIO transaction object, the construction of the first PIO transaction object includes referencing a PIO enabler object, wherein the PIO enabler captures PIO operational parameters specific to the device manager and is constructed before the construction of the first PIO transaction object, initializing data in the first PIO transaction object, the data initialized on the first PIO transaction object is particular to the input/output request, and processing the first PIO transaction to completion in conjunction with transitioning the first PIO transaction object through processing states the first PIO transaction object, wherein the transitioning comprises calling a programming interface of the first PIO transaction, the programming interface selected from a set including: PIO Transaction Execute, PIO Transaction Completed, PIO Transaction Get Bytes Transferred, or PIO Transaction Release.
 15. The system of claim 14, the device manager is a kernel-mode device driver.
 16. The system of claim 14, further comprising: a second PIO transaction object, wherein the device manager is further configured for initializing data in the second PIO transaction object and for processing a second PIO transaction to completion in conjunction with transitioning the second PIO transaction object through processing states.
 17. In a computing environment, a method for preparing the computing environment for structuring a programmed input/output (PIO) transaction, the method comprising: employing a processor executing the computer-executable instructions retained in memory to effect the following: receiving a request from a device for a programmed input/output (PIO) transaction; constructing a PIO enabler object that captures general PIO operational parameters and manages underlying operating system objects; initializing data in the PIO enabler object, the data initialized on the PIO enabler object includes default operational information of the device from which the PIO transaction request was received; and referencing the PIO enabler object to construct a PIO transaction object based in part on the initialized data of the PIO enabler object.
 18. The method of claim 17, the device that requests the input/output transaction is a device manager.
 19. The method of claim 18, the device manager is a kernel-mode device driver.
 20. The method of claim 17, initializing data in the PIO enabler object comprises selecting a profile corresponding to the device that initiated the request for the PIO transaction.
 21. A method for preparing a computing environment for structuring a programmed input/output (PIO) transaction comprising: employing a processor executing the computer-executable instructions stored on the computer-readable storage medium to implement the following acts: constructing a PIO enabler object in response to a request for an input/output transaction from a device manager, wherein the PIO enabler object captures general PIO operational parameters and manages underlying operating system objects; initializing data in the PIO enabler object from a profile that includes default information specific to the device manager that requested the input/output transaction the default information comprises at least one of alignment requirements of the device, a maximum length parameter for the transaction or maximum scatter and gather elements; and referencing the PIO enabler object to construct a PIO transaction object, wherein the construction of the PIO transaction object further includes parameters particular to the request for the input/output transaction.
 22. The computer-readable medium of claim 13, the general PIO operational parameters are associated with the device manager making the work request.
 23. The system of claim 14, wherein the programming interface of the first PIO transaction is an application program interface (API).
 24. The method of claim 17, further comprising initializing data in the PIO transaction object, the data selected from a set including: the PIO transaction, a direction of the PIO transaction, an offset into a buffer containing data to be transferred for the PIO transaction, or a length of data to be transferred for the PIO transaction.
 25. The method of claim 17, further comprising processing the PIO transaction to completion in conjunction with transitioning the PIO transaction object through processing states, wherein the transitioning comprises calling an application program interface (API) of the PIO transaction object, the API of the PIO transaction object being selected from a set including: PIO Transaction Execute, PIO Transaction Completed, PIO Transaction Get Bytes Transferred, or PIO Transaction Release.
 26. The method of claim 21, wherein the parameters particular to the request for the input/output transaction included with the PIO transaction object are data selected from a set including: the input/output transaction, a direction of the input/output transaction, an offset into a buffer containing data to be transferred for the input/output transaction, or a length of data to be transferred for the input/output transaction.
 27. The method of claim 21, further comprising processing the input/output transaction to completion in conjunction with transitioning the PIO transaction object though processing states, wherein the transitioning comprises calling an application program interface (API) of the PIO transaction object, the API of the PIO transaction object being selected from a set including: PIO Transaction Execute, PIO Transaction Completed, PIO Transaction Get Bytes Transferred, or PIO Transaction Release. 